430 



NATURE 



[January i, 1920 



that the ore was deposited metasomatic;illy, as 

 Mr. Smith asserts ; he has, however, avoided 

 the more difficult question, namely, whether the 

 ore was first deposited as a carbonate or as a 

 hydrate, and afterwards metamorphosed to red 

 haematite, or whether it was deposited in prac- 

 tically the same form as we now find it. He 

 concurs in the generally received opinion that the 

 iron-bearing- solutions were introduced from above, 

 but says nothing as to the theory strongly held 

 by many that these solutions were the result of 

 the leaching out of iron from the New Red Sand- 

 stone, which may be presumed at one time to 

 have overlain the whole of the iron-bearing region. 

 The greater part of the book is taken up with 

 a careful, detailed description of the mines, the 

 area being, for the sake of convenience, divided 

 into the Egremont and Whitehaven districts of 

 Cumberland, the Furness district of Lancashire, 

 and the far less important occurrences in the Lake 

 district. Existing mines are fully described under 

 the heads of geological occurrence and mining 

 details, whilst information as to the old and aban- 

 doned mines has also been collected. The volume 

 forms a very valuable and welcome addition to 

 our knowledge of this important mineral area. 



Vol. X., by Prof. Sibly, is geologically the most 

 important of the three, as it has involved a care- 

 ful geological study of the Forest of Dean coal- 

 field, with which the iron ores of the Forest are 

 necessarily closely connected. Much new matter 

 has thus been brought to light, and as a result 

 of his work Prof. Sibly has succeeded in proving 

 two important geological facts — one that the 

 Millstone Grit of the Geological Survey is m fact 

 a sandy facies of the dolomitised upper portion 

 of the Carboniferous Limestone, and the other 

 that there is an important unconformity between 

 the Coal Measures and the underlying rocks ; it 

 need scarcely be said that there is a close con- 

 nection between these two facts. This is the first 

 time that a systematic study of the iron ores of 

 the Forest of Dean has been attempted, and Prof. 

 Sibly deserves the highest praise for the manner 

 in which he has unravelled the complex problems 

 that the geology of the district presents. L'nfor- 

 tunately, this field cannot pretend to any economic 

 importance commensurate with its geological in- 

 terest. The ores, as Prof. Sibly shows, are of 

 relatively shallow occurrence, and have been prac- 

 tically worked out ; it is indeed fortunate that the 

 study of this field has not been deferred much 

 longer, for in that case there would probably have 

 been no mines open for the geologist to consider. 

 Prof. Sibly guesses the total amount of ore re- 

 serves still existing at about a million tons, but 

 it is very doubtful whether anything approaching 

 NO. 2618, VOL. 104] 



this figure will be produced here, and his con- 

 clusion "that the Forest of Dean is not far from 

 exhaustion as a source of iron ore " is fully war- 

 ranted by the facts. The second part of the 

 volume is taken up with a description of a small 

 group of iron-ore mines in the Carboniferous 

 Limestone that forms the south-eastern margin 

 of the South Wales coalfield, extending between 

 Taffs' Well and Llanharry ; out of the five mines 

 that have been active in this area, only one, the 

 Llanharry mine, is now at work, producing 

 50,000 to 60,000 tons yearly ; this mineral occur- 

 rence is fully described, and particulars are given 

 of the abandoned mines also. In a concluding 

 chapter Prof. Sibly discusses the genesis of all 

 the ores dealt with, and in agreement with most 

 other authorities he looks upon them as undoubt- 

 edly of metasomatic origin, due to descending 

 iron-bearing waters; he seems inclined to seek 

 the source of the iron in the Triassic rocks that 

 once probably' covered the Forest of Dean area and 

 in the Conglomerates and Red Marls of the 

 Keuper in the South Wales district. The volume 

 contains a mass of interesting information upon 

 the area studied, and as regards the Forest of 

 Dean must rank high as a piece of first-class geo- 

 logical research. 



Vol. ix. includes a number of miscellaneous 

 occurrences in different parts of the count-y, 

 of very various character. It is greatly to be 

 regretted that it falls very far below the high 

 standard to which the other two volumes have 

 attained. It is not improbable that the time 

 allotted to the investigation of each deposit was 

 insufficient, but, whatever be the cause, there are 

 no signs of the painstaking thoroughness which 

 characterises the work already discussed. This 

 voluipe leaves the impression that the authors 

 merely accepted what they were told in each case, 

 and did little actual field work, or, at the best, 

 only looked at what was shown them. They have 

 thus in many cases arrived at a wholly exagger- 

 ated opinion of the importance of the deposits they 

 describe. Yor instance, in describing the Shark- 

 ham iron-ore mine, the authors state that "the 

 amount of ore in sight is considered to be large," 

 whereas as a matter of fact there is very little 

 ore in sight, and they seem never to have heard 

 of the deep adit driven in below the deposits, 

 which runs wholly in barren limestone, and shows 

 that the occurrence is strictly limited in depth. It 

 would serve no useful purpose to multiply ex- 

 amples of such oversights ; it is, however, for- 

 tunate that none of the occurrences described in 

 vol. ix. have any real economic importaiice. 



The Geologial Survey and the countrv may both 

 fairly be congratulated on the continuation of Sir 



